Control mechanism for pumps and associated press circuits



' w. ERNST 1,952,663

CONTROL MECHANISM FOR PUMPS AND ASSOCIATED PRESS CIRCUITS March 27, 1934.

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March 27, 1934; w ERNST 1,952,663

CONTROL MECHANISM FOR PUMPS AND ASSOCIATED PRESS CIRCUITS Filed Jan. 6, 1932 2 Sheets-Sheet 2 Summer,

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Patented Mar. 27,1934

I CONTROL MECHANISM FOR PUMPS AND ASSOCIATED PRESS CIRCUITS Walter Ernst, Mount Gilead, Ohio, assignor to The Hydraulic Press Manufacturing Company, Mount Gilead, M0

' Application January 6,1932, Serial No. 585,092

13 Claims. (Cl. 138-17) This invention relates to control mechanism for pumps and more'particularly to mechanism for controlling the rate of discharge of variable delivery pumps connected or adapted to be connected in circuit with hydraulic presses.

Pumps of this general description are of various constructions, and, generally stated, the present invention relates to control mechanism adapted for use in connection with a number of diflerent types of variable discharge pumps. For the purposes of illustration one embodiment of the invention will be disclosed in connection with a pump of the radiaLreversible, variable discharge kind'now well known in the art.

Pumps of this kind are exemplified by the pump disclosed in United States Letters Patent 1,250,- 170, granted to Hele-Shaw et al., December 18, 1917. Briefly stated, such pumps include a plurality of radially arranged cylinders and pistons,

2| the rate and direction of discharge efiected by which depend upon the eccentricity of the cylinder and piston assembly relative to a drive shait.

The cylinders are usually carried by a floating,

ring or the like, which, by means of a cross head 5 or other control element, may be shifted to vary the eccentricity of the cylinders and thereby to effect control of the pump discharge. Various other kinds of variable discharge pumps are known in the art, and it will be understood that 33 the present invention relates to control mech-,

cross head in one direction wherein maximum discharge is effected, and a pressure-operated plunger arranged to be responsive to the pressure of fluid discharged by the pump for moving the cross head and associated pump elements in opposition to the spring to cut down the rate of discharge when the pressure builds up. Control mechanism of this character has certain disadvantages when used in connection with pumps serving presses performing certain operations. When using such control mechanism, the pressure of the fluid discharged by the pump will build up very rapidly as soon as the press platen engages the work, especially if there is little yield to the material being pressed. Then, when the maximum pressure is attained. the pump cross head will be forced quickly to neutral. This quick action is detrimental in many cases, for instance, where the material pressed is bakelite.

Such material is usually pressed or molded when in the powdered state, and has practically no yield. Moreover, the farms into which bakelite is molded are frequently very intricate. Hence, if. it .is attempted to build up pressure very rapidly on such material, it will not flow, but will crowd .in certain parts of the molds and will eventually break the latter, or will at least spoil the product. Also, when making laminated glass, if the press ram is run to the work rapidly and full pressure 66 immediately applied, breakage of the material is likely to result. In order most effectively to perform the operations referred to and others of a similar nature, it is desirable that the control mechanism be adapted to efiect a rapid advance 70 of the platen to the work, then a very slow and gradual building up of pressure, and finally. the reducing of the pump discharge to zero when the maximum desired pressure has been exerted upon the work.

Another disadvantage of the conventional spring and plunger control commonly used at the present time results from the fact that a pump equipped with such control mechanism will overrun the maximum pressure for which the mechanism is-set. This is due to the fact that there is a certain amount of inertia in the control mechanism parts, so that, when the press platen en'-' counters sudden resistance, the pressure will build up so rapidly that the plunger and associated elements of the control mechanism will not force the pump cross I head to neutral position quickly enough. As a result, the discharge pressure will overrun the maximum for which the mechanism is set, and subsequently will drop below this maximum pressure. This results in a fluctuation of 'that improved operation of the latter is efiected.

Other objects will become apparent from a reading of the following detail description, the appended claims, and the accompanying drawings.

Figurel is a view partly in front elevation and partly in vertical section of a pump and control mechanism arranged in accordance with the invention, a hydraulic circuit to which the pump is connected being shown diagrammatically;

Figure 2 is a top plan view of the pump and control mechanism shown in Figure 1, with certain parts broken away;

Figure 3 is a vertical sectional view of a casing member of my improved control mechanism and showing certain parts therein in difierent positions from those shown in Figure 1; and

Figure 4 is a vertical sectional view of a control mechanism casing showing a modified form of piston packing.

.A practical embodiment of the invention is illustrated in the accompanying drawings, which show a pump A provided with mechanism constructed in accordance with the invention and connected in circuit with a hydraulic press B. The pump Ashown for the purposes of illustration is of the radial variable discharge type, and includes a casing 1 and a shaft 2 which may be driven from any suitable source of power.

The press B connected in circuit with the pump is likewise of a conventional type and includes a base 3, a press head 4 connected tothe base by means cf strain rods 5, a platen 6 guided for reciprocation on the strain rods, and a double acting ram 7 connected to the platen 'for reciproeating the latter and being mounted in a cylinder 8. The lower end of the cylinder constitutes a pressing chamber 9 to which fluid is delivered under pressure for causing the ram and platen to perform a pressing stroke, and the upper end of the cylinder constitutes a ram-returning chamber 10 into which fluid is delivered under pres- The pump is arranged to draw fluid from a tank C by means of an intake pipe 11 connected between thetank and the intake side of the pump, and to discharge fluid under pressure through a pump discharge pipe 12 which leads to a four-way control valve D. 'The valve D is of the conventional rotary plug four-way type and includes a casing 13 formed with spaced ports, 14, 15, 16, and, 17, and a rotary plug 18 formed with passages 19 and 20 adapted to connect the aforenamed ports inthe manner desired for efiecting flow to and from the press.

A delivery pipe 21 provides communication between the port 15 of the valve and the lower or pressing chamber!) of the press cylinder, and a second delivery pipe 22 provides communicationbetween the port 17 of the valve and the upper or ram-returning chamber 10 of the press cylinder. A return pipe 23 provides communication between the port 16 of the valve and the tank C. When the valve rotor is in the position shown in Figure 1, fluid discharged by the pump will' flow through the pipe '12, the port 14 of the valve D, the passage 19 in the valve rotor, the port 15, the delivery pipe 21, and thence into the pressing chamber 9, thereby moving the ram '7 and platen 6 upwardly to bring the mold members a. and b into cooperative relation. During upward movement of the ram, fluid contained in the ram-returningchamber 10 will flow out through the pipe 22, the port 17 in the valve, the passage 20 therein, the port 16, the return pipe 23, and thence'into the tank C. When the valve rotor is moved through ninety degrees in a counterclockwise direction, the passage 19 will connect the ports 15 and 16, and the passage '20-will connect the ports 14 and 17. Fluid discharged by the pump will then be directed through the pipe 12,'the port 14, the passage 20, the port 17, and the delivery pipe 22 into the ram-returning chamber 10 of the press cylinder for positively driving the ram and platen downwardly. During the return stroke of the ram, fluid contained in the pressing chamber 9 will flow out through the pipe 21, the part 15, the passage 19, the port 16, and the return pipe 23 to the tank C. Although the press shown is of the upward acting type, it is desirable that the ram and platen be positively driven down because of the fact that, in some cases, the mold members a and b have a tendency to stick together after the' pressing and curing operation has been completed, and the weight of the ram and platen cannot be relied upon to return thes parts to their lower positions.

As shown in Figure 2, the pump A includes a pair of floating rings 24-24 mounted in the easing 1, these rings being movable radially with respect to. the pump shaft for varying the pump discharge. Rods 25-25 are connected to the rings 24-24 and extend through the casing at 26-26, the outer ends of the rods being connected by a cross head or pump flow control element 27 secured to the rods by nuts 28-28. Rods 29-29, also 'connected to the rings 24-24, extend through the opposite side of the casing at 30-30, the outer ends of these rods being connected by across head'31 secured to the rods by nuts 32.

The illustrative embodiment of the control mechanism constructed in accordance with the present invention includes a bracket 33 connected to the right hand side of the pump casing as viewed in Figures 1 and 2, the outer end of the bracket being formed with a bore 34 in whichis journalled a spindle 35 extending inwardly toward the cross head 27.- A thrust bearing 36 is interposed between a collar 37 on the spindle and the adjacent end of the bracket 33. The inner end of the spindle is threaded as at '38 for cooperation with an internally threaded travelling nut 39, and a spring 40, interposed between the nut 39 and a spring seat 41 which bears against the pump cross head 27, serves to urge the cross head '27 and the associated floating rings 24 to the left so as to efi'ect maximum discharge through the pipe 12. A hand wheel 42 secured on the outer end of the spindle 35 serves to rotate the spindle and to position adjustably the nut 39 thereon so as to vary' the loading of the spring 40 and thereby to vary the force by which the cross head 2''! and connected parts are urged to the left.

A casing member 43 containing mechanism for moving the cross head 31 and the floating rings 24 to the' right against the urge of the spring 40 is provided with spaced legs 44-44 which are adapted to straddle the cross head 31 and which are secured to the pump casing by means of bolts 45. This casing is formed with a. bore 46 terminating in a cylinder 47, and a relatively small piston or plunger 48 extends through the bore 46 and through packing 49 held in the bore by means of a gland nut 50. The inner end of the piston is connected to the cross head 31, and the outer end of the piston extends into the pressure cylinder 47. This cylinder is in constant communication with the discharge pipe 12 by means of a pipe 51, so that the unit pressure existing in the cylinder 4'? and hence the unit pressure acting on the piston 48 will always be the same as the pump'discharge pressure.

To the left of the cylinder 4'7 the casing 43 is formed with a larger cylinder 52 coaxial -with the cylinder 47 and the inner end of which is counterbored at 53 to provide a resultant shoulder 54. The outer end of the cylinder 52 is closed by an end plate 55, and the inner end of the cylinder is separated from the cylinder 4'7 by means of a. partition 56. Mounted in the large cylinder 52 is a relatively large piston 5'7 formed with a central opening 58 in which a bushing 59 is positioned. The bushing is formed at its inner end with a flange 60 which serves as an abutment with which the piston 5'7 engages when the piston is forced to the right in a manner to be described later. The bushing 59 is adapted toslide in an opening 61 in the end plate 55, and packing 62 held in place by means -of a gland nut 63 prevents leakage from the cylinder'52. 5

A push rod 64 extends through the bushing 59 and has threaded engagement therewith at its outer end so that'it may be adjusted relatively .to the bushingfand consequently may be adjusted relatively to the piston 57 for a purpose to be explained later. A cap nut 65 serves both to cover the outer threaded end of the push rod 64 and to lock the latter in adjusted posi tion. The inner end of the push rod is formed with an enlarged part 66 providing a resultant shoulder 6'7 with which the inner end of the bushing 59 is adapted to engage, and the enlarged part 660i the push rod extends through an opening 68 in the partition 56 for engager ment with the outer end of the smaller plunger '43. It should be noted, however, that the push rod 64 is not connected tothe piston 48 in such a way that outward movement of the push rod will efiect an outward movement of the piston 48. There is no two-way driving connection between the piston 5'7 and the piston 48, and it is only by contacting engagement of the inner end of the push rod 64 with the piston 48 that movement of the latter-is efleeted when the piston 5'7 is moved. In other words, the piston 5'7 is movable independently of the piston '48except when the piston 52 is moving toward the right and the push rod is in engagement with the piston 48. I

A pipe 69 provides constant communication between the pressing chamber 9 of the press B and a passage '70 leading to the cylinder 52, so that the unit pressure existing in the cylinder 52 and acting on the relatively large piston 5'7 will always be the same as that existing "the pressing chamber 9. A pipe '71 provides onstant communication between the tank C and a passage 72 leading tothe right hand end of the cylinder 52.

In order that the sequenceof operations of the press ram and the various pump control elements be readily understood, a complete operating cycle of the press will be set forth briefly. It will be assumed that the various parts are in the positions shown in Figure '1. The pump will deliver fluid under pressure through'the pipe 1 2,

(is the control valve D, and the pipe 21 to the presstake place, and the ram and platen will be moved up rapidly. a

At this time the unit pressure existing in the cylinder 4'7 and acting on the piston 48, and the unit pressure exist'ng in the cylinder 52 and acting on the piston 5'7 will be equal to the pump discharge pressure, which, as staied above, is only suflicient to raise the ram and platen, so that the pistons 48 and 57 will not move the cross head 31 and floating rings 24 appreciably against the urge of the spring 40. When the mold member b first engages the material to be molded, pressure will begin to build up in the pressing chamber 9 and the pump discharge pipe 12. This will result in a corresponding building up of pressure in the cylinder'52 and the cylinder 47, and, since the pump discharge pipe is connected to the pressing chamber, the pressures existing in the cylinders 52 and 4'7 will be the same. When the unit pressure has built up to a predetermined extent in the cylinder 52, the total pressure acting upon the large piston 57 will be suflicient to move the latter toward the right, thereby also moving toward the right the bushing 59 and the push rod 64, wh ch will force the'piston 48 toward the right to move the pump cross head 31 and the floating rings 24 toward their neutral positions against the urge of the spring 40, which constantly tends to hold the floating rings in their extreme left hand position. The movement of the p.ston' 57 will be arrested by engagement of the latter with the shoulder. 54 in the casing 43. this shoulder constituting a. stop for the piston 5'7, so that the movement of the floating rings effected by the piston 5'7 will be limited, and, although serving to reduce the rate of pump discharge, will not move the floating rings to their neutral positions. At this time the pistons 5'7 and 43 will be in the positions shown in Figure 3,

wherein the piston 5'7has reached the limit of reduced to zero in the mannerdescribed above,

the valve rotor 18 will be rocked in a countel-clockwise direction to place the pump discharge pipe 12 n communication with the delivery pipe 22 and to place the return pipe 23 in communication with the delivery pipe 21.- The cylinder 52 of the control mechanism will still communicate with the pressing chamber 9, wh ch, at this time, is connected to the tank C, so that the pressure existing in the cylinder 52 will be low. The pump will then deliver fluid under pressure through the pipe 12, the valve D, and the pipe 22 to the'ram-returning chamber 10 so as positively .to drive the ram and platen downwardly. At this time the spring 40 will hold the cross head 2'7 and the floating rings 24 in their extreme left hand positions so as to effect maximum discharge by the pump. Inasmuch as the cylinder 52 communicates with the tank Cbyway ofthe pressing chamber 9, no pressurecan build up in this cylinder to oppose the action et the spring 40. In case the mold members afiid I) stick, it may be necessary to apply imme lately the full pump pressure .to'separate the molds quickly. If the molds a. and I) stick, so as to re- 15g l sist downward movement of the ram 7, pressure will begin to build up in the ram-returning chamber 10 and the discharge pipe 12 immediately. Since the cylinder 52 is not in communication with the discharge pipe or with the ram-returning chamber, there will be no building up of 'pressure in this cylinderat this time. Consequently,

pressure will continue to build up in the ram-returning chamber until sufficient pressure is exerted upon the ram to separate the mold members, or, if the mold members can not be thus separated, the discharge pressure will finally build up to a degree suificient to move the small piston 48 to the right against the urge of the spring 40 to reduce the pump dscharge to zero and to prevent breakage of any parts. After sumcient pressure has acted upon the ram to separate the mold members, the ram and platen will'descend freely and the pump discharge pressure will reduce, so that the spring 40 will be enabled to move the cross head 27 and the rings 24 to the left to effect a maxmum rate of flow through the pump and a quick return of the ram and platen.

It will be noted that the pistons 57 and 48 serve to provide two pressure-limit controls for any given loading of the spring 40. The piston 57 functions first during a building up of pressure in the main cylinder to -reduce the pump discharge to a predetermined value without reducing it to zero, and the piston 48 functions subsequently during a further building up of pressure to reducethe pump discharge to zero. The amount of initial reduction of the pump discharge effected by the piston 57 can be adjusted by varying the extent to which the push rod 64 projects inwardly from the bushing 59, this serving to vary the efiective length of stroke of the piston 57. Thus, if the push rod 64 is so adjusted as to contact with the piston 48 when the piston .57 and bushing 59 are in their extreme left hand positions, a maximum movement of the piston 48 will be effected by travel of the piston 57 from the left hand end of the cylinder 52 to the right hand end thereof. If the push rod 64 is adjusted inwardly relative to 'the bushing 59 until the shoulder 67 contacts with the inner end of the bushing 59 when the piston 57 is in its extreme right hand position in engagement with the shoulder 54, no movement of the piston 48 can be effected by the piston 57. Obviously, the push rod 64 may be adjusted'to any number of intermediate positions relative to the bushing 59 so that the control mechanism can be adjusted to efiect a partial reduction of pump discharge pressure to any desired amount. The low pressure control can be so adjusted as to efiect cutting down of the discharge to a very small amount, which-will efiect a gradual building up of pressure to'its maximum as distinguished from a sudden building up of pressure, as is effected by prior control mechanisms.

The control mechanism is quite sensitive and is capable of effecting a very fine control of pressures. I have found that the packing friction exerted upon the piston-48 has considerable effect upon the operation of the mechanism, and, in orderto take full advantage of the sensitive characteristics of the mechanism, I have provided a modified form of packing for the piston formed adjacent its inner end with a pair of' spacedannular grooves 73- 73 in which is positioned a pair of soft felt packing rings 74-74 which contact with the piston 48. A drainage groove 75 is formed in the bore 46 intermediate the cylinder 47 and the packing ring grooves 73, and a passage 76 leading from the drainage groove is adapted to be connected to the tank by means of a pipe 77. Any fluid which leaks from the cylinder 47 between the bore 46 and the piston 48 will be collected in the drainage groove 75 and will flow from this groove through the passage 76 and the pipe 77 to the tank 0. Because of the communication of the groove 75 with the tank, it is not possible for fluid under high pressure to reach the packing rings 74, so that these rings need not bear tightly upon the piston 48, and the latter is therefore freely slidable within the bore 46 with a minimum of friction.

While the control mechanism herein shown and described embodies the invention in a practical form, it is to be understood that various changes may be made in the specific construction and arrangement of parts without departing from the spirit of the invention as defined inthe claims.

I claim:

1. Control mechanism for a variable discharge pump having a shiftable flow control element, said mechanism comprisfng means for urging said flow control element in one direction; a cyl- 0 inder; a relatively small piston mounted therein for reciprocation in the direction of shifting pof said flow control element and being adapted to move the latter in the opposite direction; a second cylinder; a push rod mounted for sliding 11 movements towards and from said smaller piston for engagement therewith to move it and said flow control element in said opposite direction; a bushing surrounding said push rod and extending exteriorly beyond said second cylinder and having threaded connection with said push rod whereby said push rod can be adjusted longitudinally of said bushing; and a relatively large piston mounted on said bushing and being slidable in said second cylinder.

2. Control mechanism for a variable discharge pump having a shiftable flow control element, said mechanism comprising means for urging said flow control element in one direction, 8. casing member; a cylinder therein; a bore in said 1 5 casing extending inwardly from said cylinder; a piston mounted for sliding movements in said bore and extending inwardly from said cylinder for connection with said flow control element for shifting the latter in the opposite direction: a soft packing ring mounted in said bore and surrounding said piston; a drainage groove in said bore intermediate said cylinder and said packing ring; a second cylinder in said casing member aligned coaxally with said first cylinder, said groove and said packing being located inwardly beyond saidcylinders; a piston mount ed therein for reciprocation towards and from said first piston for engagement with the latter to shift it and said flow controlelement in said opposite direction; and a stop for limiting shifting movement of said second piston in said opposite direction.

3. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a .variable discharge pump having a shiftable flow control element; means forming a hydraulic press-operating circuit with said pressing chamber, said said larger piston before said smaller piston has rain-returning chamber, and said pump; and control mechanism for said pump comprising means connected to said flow control element for urging it in one direction, two pressure cylinders, two separate and relatively movable pistons respectively mounted in said cylinders, each of said pistons being adapted to shift said flow control element in the opposite direction, a hydraulic connection between one of said cylinders and the discharge side of said pump, and a hydraulic connectionbetween the other cylinder and only ment in the opposite direction, and means responsive to pressure in only one ot'saidscylinder chambers for moving said flow control element in said opposite direction.

-5. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a variable discharge pump having a shiftable flow control element; means forming a hydraulic press-operating circuit with said pressing chamber, said ramreturning chamber, and said pump; and control mechanism for said pump comprising means connected to said flow control element for urging it in one direction, a first control cylinder, a hydraulic connection between said cylinder and the discharge side of said pump, a relatively small piston mounted for reciprocation in said cylinder, a second control cylinder, a hydraulic connection between said second control cylinder and the pressing chamber of said press cylinder, and a relatively large piston mounted in said second control cylinder for movements independently of said smaller piston, each of said pistons having driving connection with said flow control element for shifting the latter in the opposite direction. J

6. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a variable discharge pump having a shiftable flow control element; means forming a hydraulic'press-operating circuit 'with said pressing chamber, saidramreturning chamber, and said pump; and control mechanism for said pump comprising means connected to said flow control element for urging it in one direction, a first control cylinder, a hyturning chamber, and said pump; and control draulic connection between said cylinder and the discharge side of said pump, a; relatively small piston mounted for reciprocation in said cylinder, a second controlcylinder, a hydraulic connection between said second control cylinder and the pressing chamber of said'press cylinder, a relatively large piston mounted in said second control cylinder for movements independently of and a stop for arresting shifting movement of moved to the limit of its shifting stroke;

7. The combination with a hydraulic ,press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a variable discharge pump having a shiftable flow control element; means forming a hydraulic press-operating circuit with said pressing chamber, said ram-returning chamber, and said pump; and control mechanism for said pump comprising means connected to said flow control element for urging it in one direct-ion, a first control cylinder, a hydraulic connection between said cylinder and the discharge side of said pump, a relatively small piston mounted for reciprocation in said cylinder, a second control cylinder, a hydraulic connection between said second control cylinder and the pressing chamber of said press cylinderfa relatively large piston mounted in said second control cylinder for movements independently of said smaller piston, each of said pistons having driving connection with said flow control element for shifting the latter in the opposite direction, Y

a stop for arresting shifting movement of said larger piston before said smaller piston has moved to the limit of its shifting stroke, and means for varying the effective length of shifting stroke of said larger piston.

8. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a variable discharge pump having a shittableflow control element adapted normally to occupy a position providing a predetermined maximum pump discharge rate; means forming a hydraulic press-operating circuit with said pressing chamber, said ram-returning cham- I bet, and said pump; and control mechanism for said pump comprising a first control cylinder, a hydraulic connection between said cylinder and the discharge side of said pump, a relatively small piston mounted for reciprocation in said. cylinder, a second control cylln'der, a hydraulic connection between said second control cylinder and the pressing chamber of said press cylinder,.a relatively large piston mounted in said second control cylinder for movements independently of said smaller piston, eachof said pistons having driving connection with said flow control element for shifting the latter to decrease the pump discharge rate, and a stop for arresting shifting movement of said larger piston before said smaller piston has moved to the limit of its shitting stroke..

9. The combination with a hydraulic press havv mechanism for said pump comprising means connected to said flow control element for urging it in one direction, means responsive to pump discharge pressure .for moving said flow control element in the opposite direction, means responsive to pressurein only one of said cylinder chambers for moving said flow control element in said opposite directiomand a stop for limiting movement of said flow control element by said last named means,

10. The combination with a hydraulic press having cylinder means including a pressing chamher and a ram-returning chamber, and reciprocable ram means therein; of a. variable discharge pump having a shiftable flow control element; means forming a hydraulic press-operating circuit with said pressing chamber, said ram-retuming chamber, and said pump; and control mechanism for said pump comprising means connected to said flow control element for urging it in one direction, means responsive to pump discharge pressure for moving said flow control element in the opposite direction, means responsive to pressure in only one of said cylinder chambers for moving said flow control element in said opposite direction, and meansfor varying the amount of shifting of said flow control element by said last named means.

11. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; and control mechanism comprising a flow control element, means connected to said element for urging it in one direction to effect delivery of fluid to said motor at a maximum rate, means responsive to pressure in only one of said cylinder chambers for moving said flow control element in the opposite direction to diminish the rate of delivery, and

' means responsive to pump discharge pressure for moving said flow control element in said opposite direction.

12. The combination with a hydraulic press having cylinder means including a pressing chamber and a ram-returning chamber, and reciprocable ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; and control mechanism comprising a flow control element, means connected to said element for urging it in one direction to effect delivery of fluid to said motor at a maximum rate, means responsive to pressure in 7 arrested movement of said first pressure responsive means. r

13. The combination with a hydraulic press having cylinder means including a. pressing chamber and a ram-=returning chamber, and reciprocable ram means therein; of pump means for supplying fluid under pressure; a shittable flow control element; means forming a hydraulic press-operating circuit with said pressing chamber, said ram-returning chamber, and said fluidsupplying'means; and control mechanism connected to said flow control element for urging it in one direction, means responsive to pump dis charge pressure for moving said flow control element in the opposite direction, and means responsive to pressure in only one 01' said cylinder chambers for moving said flow control element in said opposite direction.

ERNST. 1 

